Master Coding Skills &
System Design.

Understand JavaScript memory — stack vs heap, mark-and-sweep GC, common memory leaks (event listeners, intervals, closures) and how to fix them.

Build Segment Tree and Fenwick Tree from scratch — range sum queries, point updates, and when to use each for competitive programming.

10 SQL optimization techniques with before/after examples — indexes, covering indexes, NOT EXISTS vs NOT IN, LIMIT pushdown, and partition pruning.

Master PHPUnit — test classes, assertions, setUp/tearDown, mocking dependencies, data providers, and test coverage reporting.

Understand microservices vs monolith trade-offs, when to extract a service, the modular monolith middle ground, and migration strategy.

Master browser Web APIs — Fetch with AbortController, localStorage vs sessionStorage, IntersectionObserver for lazy loading, MutationObserver.

Master string searching algorithms — naive O(nm), KMP O(n+m) with failure function, Rabin-Karp with rolling hash, and when to use each.

Understand MySQL replication — binary log, replica setup, replication lag, routing reads to replicas and writes to master in PHP.

Complete PHP security guide — prevent XSS with htmlspecialchars, SQL injection with PDO, CSRF with tokens, and add security headers.